Resin particles are granular particles and are widely used as additives for use in other materials. They can be produced, for example, separating resin particles as a wet cake from an aqueous dispersion (latex) of resin granules dispersed in water, and drying the separated resin particles. However, such particles are susceptible to coagulation with each other upon drying or are poorly dispersed when the dried resin particles are added to other materials.
As a possible solution to prevent the coagulation of particles upon drying, Japanese Unexamined Patent Application Publication (JP-A) No. 59-155402, for example, discloses a technique for the production of a thermoplastic resin, including the steps of coagulating latex particles, removing free water, separating latex particles as a wet cake, adding a flowability-imparting agent to the wet cake, and spray drying the resulting mixture. Japanese Unexamined Patent Application Publication (JP-A) No. 59-22905 discloses a technique of granulating particles having a high bulk density and capable of absorbing a plasticizer satisfactorily, by adding a hydrophobic substance to the wet cake.
All these techniques, however, fail to sufficiently prevent the coagulation upon drying, because a flowability-imparting agent or a hydrophobic substance is added to a wet cake containing tightly adhered resin particles, does not cover entire surfaces of particles uniformly, and exposed surfaces of particles come in intimate contact with each other. In addition, the resulting resin particles have poor dispersibility, are thereby difficult to mix with other materials uniformly, and are limited, in use.    Patent Document 1: Japanese Unexamined Patent Application Publication (JP-A) No. 59-155402    Patent Document 2: Japanese Unexamined Patent Application Publication (JP-A) No. 59-22905